1. Field of the Invention
This invention relates to pesticide compositions, and more specifically to storage-stable pesticide formulations containing azadirachtin as the active ingredient.
2. Description of the Prior Art
The biological activities of the neem tree seeds have long been recognized. Of primary importance are the potent pesticidal properties of azadirachtin, the main active ingredient in the neem seed. Azadirachtin is a tetranortriterpenoid that causes feeding inhibition and growth disruption in various insect, mite, nematode, etc. orders.
There are various methods known in the prior art to extract azadirachtin from neem seeds, including the use of solvents such as methanol, ethanol, water, methylene chloride, chloroform, hexane, methylethylketone, butanol, petroleum benzene, ether, acetone, methyl tertbutyl ether, diethylcarbonate, etc. In general, it has been found that the efficiency of the extract yield can be increased by increasing the solvent polarity, i.e., from hexane to ethanol, ethanol to methanol, methanol to water, etc. However, while various studies have examined relative solvent extraction efficiencies, little attention has focused on the shelf life stability of azadirachtin in solution.
The most significant limitation to the successful use of azadirachtin as a pesticide and insect repellant is the lability of the azadirachtin in solution. One study has shown that heat and sunlight (UV radiation) cause rapid degradation of azadirachtin. J. Environ. Sci. Health,A17(1), 57-65 (1982) by J. B. Stokes and R. E. Redfern. Sunlight degradation of azadirachtin can be effectively reduced by addition of UV absorbing additives such as para-aminobenzoic acid (PABA), neem oil, angelica oil, castor oil, or calmus oil.
Other factors known to affect the storage stability of azadirachtin are the concentration of azadirachtin in solution and the pH of the solution. U.S. Pat. No. 4,556,562 (Larson) discloses improvement in storage properties of azadirachtin in aqueous ethanol emulsions by adjusting the concentration of azadirachtin in the range 2000 to 4000 ppm and adjusting the pH in the range 3.5 to 6.0.
It now has been discovered that the stability of azadirachtin in solution is decreased in the presence of protic solvents, in particular water, acids and bases.